The use of mobile communication devices including cellular telephones, pagers and wireless internet access appliances has increased exponentially in recent years. This increased demand for mobile communication devices has led to rapid growth in the infrastructure required to support these services.
A block diagram of a conventional communication network for communicating with cellular or mobile telephones or station, is shown in FIG. 1. Referring to FIG. 1, a conventional communication network 10 for communicating with a mobile station 12 typically includes a mobile switching center (MSC 14) that communicates with a public switched telephone network (PSTN 16) and a number of base station controllers (BSC 18), only one of which is shown. Each BSC 18 in turn communicates with one or more base transceiver stations (BTS 20). The BTS 20 are coupled via a feed cable 22 to one or more antennas 24 mounted on top of a tower 26 and are responsible for transmitting and receiving communication signals between the communication network 10 and the mobile station 12. Each BTS 20 commonly includes one or more transceivers for transmitting and receiving signals, amplifiers for amplifying received and transmitted signals, a duplexor for applying transmitted signals to the antenna 24 and split the received signals onto a receive line, and a backhaul for coupling signals between the BTS and the BSC 18. The mobile switching center 14 operates as the nerve center for the entire network and communicates with the BSC 18 using an established protocol such as, for example, the GSM (Global Systems for Mobile Communications) protocol, the CDMA (Code Division Multiple Access) and the TDMA (Time Division Multiple Access) protocols. These various protocols dictate the nature of the communications between the MSC 14, the BSCs 18, and the BTSs 20 and are well known to those skilled in the art.
Conventional BSCs 18 are primarily responsible for dictating the size of an associated cell. That is, the area covered or served by a particular BTS 20. There are no fixed specifications as to the size of the cells, but in current usage, it is common to refer to macro cells, mini cells, micro cells and pico cells. The range of the various cells tends to vary with their size and by way of example in current usage, macro cells typically have antennas 24 that output on the order of 20-50 watts of energy and tend to have ranges on the order of 5-40 kilometers. Mini cells typically have power outputs on the order of 10 watts and corresponding ranges in the vicinity of 2-5 kilometers. Micro cells typically have power consumption on the order of 2-8 watts with ranges of a kilometer or so. Of course as signal processing capabilities in antenna designs improve, the distinction between the various sizes blurs but in concept, the cell size may always be varied.
One problem frequently encountered by conventional communication networks having the antenna 24 on top of the tower 26 arises from the feed cable 22 coupling communication signals between the BTS 20 and the antenna. In the illustrated arrangement, the antenna 24 is mounted on the top of the tower 26 while the associated BTS 20 is at the base of the tower. Thus, if the tower 26 is tall, a long feed cable 22 must be provided between the BTS and the antenna 24. Moreover, often the BTS 20 is located some distance away from the tower 26 in a location more protected from the environment or more readily accessible by maintenance personnel, further lengthening the feed cable 22. Generally the feed cable 22 includes a pair of coax cables with one coax cable (a transmit line) being arranged to carry the transmit signal and one coax cable (a receive line) being arranged to carry the receive signal. Often, the transmit and receive line can be combined in a single multiplexed feed cable 22. A long feed cable 22 presents several difficulties including significant signal intensity or power losses in both received and transmitted signals, and signal degradation by the introduction of noise to the received signal.
Another problem with conventional communication networks is the difficulty in upgrading or modifying the BTS 20 hardware to alter size and/or shape of a particular cell. For example, as wireless communication technology increases in popularity it is often desirable to reduce the size of a cell to permit the introduction of additional cells in order to handle higher usage. In other instances it is desirable to increase the size of a cell to provide improved range. Although the present designs work well, they are not particularly modular in that if it is desirable to change the size of a cell for any reason, it is necessary to replace the entire BTS 20, rather than just an amplifier, duplexor, backhaul or transceivers contained therein. Conventional BTSs 20 are relatively large and expensive units. Thus, it is desirable to provide a BTS architecture that enables the BTS components to be upgraded, repaired or replaced independently and even reused if the reason for replacement was merely to change cell size or cell geometry.
The present invention provides a solution to these and other problems, and offers other advantages over the prior art.